Carrying amount as of the balance sheet date, which is the cumulative amount paid and (if applicable) the fair value of any noncontrolling interest in the acquiree, adjusted for any amortization recognized prior to the adoption of any changes in generally accepted accounting principles (as applicable) and for any impairment charges, in excess of the fair value of net assets acquired in one or more business combination transactions.

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+ Details

Note 3 - Merger with Nicor (Detail) - Allocation of Total Goodwill (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Goodwill	$ 1,817	$ 1,813	$ 418
Distribution Operations [Member] \| AGL Resources' Legacy Goodwill [Member]
Goodwill	400
Distribution Operations [Member] \| Merger With Nicor [Member]
Goodwill	1,191
Distribution Operations [Member]
Goodwill	1,591	1,586	404
Retail Operations [Member] \| AGL Resources' Legacy Goodwill [Member]
Goodwill	0
Retail Operations [Member] \| Merger With Nicor [Member]
Goodwill	122
Retail Operations [Member]
Goodwill	122	124	0
Midstream Operations [Member] \| AGL Resources' Legacy Goodwill [Member]
Goodwill	14
Midstream Operations [Member] \| Merger With Nicor [Member]
Goodwill	0
Midstream Operations [Member]
Goodwill	14	16	14
Cargo Shipping [Member] \| AGL Resources' Legacy Goodwill [Member]
Goodwill	0
Cargo Shipping [Member] \| Merger With Nicor [Member]
Goodwill	90
Cargo Shipping [Member]
Goodwill	90	77	0
AGL Resources' Legacy Goodwill [Member]
Goodwill	414
Merger With Nicor [Member]
Goodwill	$ 1,403